In order to reduce the weight and the cost of the blades of turbine engine fans, they are generally made out of composite material. Fan blades need to be capable of withstanding high levels of shock and impact because of their speed of rotation and because of collisions with particles or foreign bodies that may penetrate into the stream of air. For this purpose, composite blades are protected at their leading and/or trailing edges by metal reinforcement that is adhesively bonded to the airfoils of the blades.
Document EP 1 547 270-A1, in the name of the applicant, describes a method of fabricating such reinforcement by superplastic forming and diffusion bonding (SPF/DB), which method consists in:                bonding two pieces of sheet metal together by diffusion bonding in order to obtain a preform, some portions of the pieces being covered in an anti-diffusion substance in order to prevent them bonding together in determined zones;        curving and twisting the preform;        inflating the preform so that it is subjected to superplastic forming; and        cutting the preform in order to obtain the reinforcement.        
That method does not make it possible to control the inside shape of the cavity in the reinforcement with accuracy. In particular, the junction zones between the pieces of sheet metal form stress concentration zones where break starters weaken the reinforcement.
In order to improve the mechanical strength of the reinforcement, patent application FR 10/51992, filed by the applicant and not yet published, proposes a method of making metal reinforcement, which method consists in:                shaping two pieces of sheet metal in order to bring them close to the final shape of the reinforcement that is to be made;        positioning the two pieces of sheet metal on either side of a core reproducing the inside shapes of the suction side and of the pressure side of the reinforcement;        assembling the two pieces of sheet metal together around the core in leaktight manner under a vacuum;        shaping the pieces of sheet metal on the core by hot isostatic compression; and        cutting the pieces of sheet metal in order to separate the reinforcement and release the core.        
Hot isostatic compression enables the pieces of sheet metal to be shaped to have the same shape as the core, thus making it possible in the junction zone between the pieces of sheet metal to obtain a large radius of connection and consequently to avoid any zone of stress concentration or of break starters.
Prior to being positioned around the core, the shaping of the pieces of sheet metal is performed in a plurality of successive hot-forming operations.
Nevertheless, it is difficult to control accurately the shape, the thicknesses, and the surface states of the sheet metal pieces as formed in that way. In addition, the duration and the cost of such operations are relatively high. Finally, the shaped pieces need to be machined after forming, which is particularly difficult and expensive when they present a three-dimensional profile. It is easier to machine sheet metal while it is plane, i.e. before it is shaped.